Testing Tank Flushing Systems in the Clear RV Black Tank!

My first Black Tank Simulator experiment turned out to be pretty popular. If nothing else, it was unique, and I don’t think anyone had tried it before. I got plenty of suggestions for ways to make the experiment better. Many of these suggestions were good, and I incorporated them into this experiment. One of them, it turns out, makes a huge difference in how things go.

In this video, I walk you through some of the changes I’ve made to the experiment setup, and then I proceed with four runs to test the following products:

First, I want to say that I am ONLY looking at the TANK FLUSHING PERFORMANCE in these tests. I know that the Sewer Solution can do other things like pump uphill. I know that the Tornado Rinser requires you to modify your RV to use it. But for now, I’m just focused on one thing: How well will each of these products flush out your RV black tank?

Having run the tests, I have to say, I was a bit surprised and enlightened by the results. Even Stef got pretty interested in how things were turning out, because they weren’t quite what we expected. I know the video is super long, but I didn’t feel I could cut much more out without taking away some valuable footage.

At any rate, when the tests were all done, and I had a chance to think about it for a while, I came up with the following conclusions:

Conclusion 1:

Your plumbing configuration makes a big difference. Just two simple 45 degree elbows completely change the effectiveness of a “Drain End” flush system. So the first thing I’m going to recommend is to stick your head under your RV and check out how your plumbing flows from your black tank to the gate valve and outlet. Knowing this will help you pick out a tank flushing system that will work for you.

Conclusion 2:

The clear section you may have added to your drain setup is likely lying to you. This is still somewhat dependent on plumbing, but in all cases – the water was sparkly clean in the clear section before the tank was completely clean. If you’re going to buy one of these clear gadgets so you can tell when your tanks are clean, don’t bother… they’re not.

Conclusion 3:

The “Drain End” flush systems without a way to shut off the flow out of the tank are completely worthless unless you have a straight shot back into the tank. The water won’t make it back into the tank, and you’re just cleaning out the piping until the first bend. They just waste water. Don’t bother.

Conclusion 4:

Even when you can shut off the flow, the “Drain End” flush systems are no more effective than just filling the black tank (again, unless you’ve got a completely straight shot back into the tank). Don’t waste your money. You can fill the tank by flushing the toilet, or, depending on your RV, by using a bathroom faucet that drains to the black tank – and then you won’t have any additional pieces of sewage-contaminated equipment to worry about handling. If you’ve ever looked at one of my RV review checklists – now you know why “does the bathroom sink drain to the black tank” is on there. It’s easy, it’s convenient, and it works just as well as almost anything else out there.

Conclusion 5:

The only system that cleaned the walls with any real effectiveness was the Tornado Rotary Tank Rinser. I’ll generalize and say those results are probably similar for any built-in rinsing system. The in-tank rinsing system can also do anything a “drain end” system can do. The downside here is that unless your RV came with one, you have to drill a hole in your black tank to install it. I’m not sure I’m willing to go there yet. But if your coach came with a rinse system… use it.

And Finally:

If something is heavy enough to sink to the bottom of the tank, you’re probably not going to get it out of there, except perhaps by luck. Some of the “simulated waste” in each of the runs would settle on the bottom and just sit there. Whether or not it made it out was simply “luck of the draw”. One reader has already suggested that this highlights the importance of alwaysleaving a bit of water in the black tank to keep the inevitable leftovers from “hardening”. I couldn’t agree more.

So What’s Next?

That settling waste leads me to what I think will be my next experiment… tank treatments. From watching this video, it’s pretty apparent that getting waste consistently liquefied, and fast, is key to getting it out of the tank. So for my next experiment, I’m going to test some tank treatments to see which one does that the best.

That experiment will take a while to set up and carry out. I’ll have to figure out a way to keep the tank indoors (to eliminate any temperature and lighting effects). I’ll need to generate simulated waste that’s even more similar to the real thing, because now we’re getting into chemistry. And I’ll need to run the experiment for days at a time to give the treatments time to work (and because that’s how we use our RVs). I’ll be working on these challenges, and I will get it done eventually.

The test run sheet with my procedure is attached just below. Hope you enjoy the video. Cheers!

Full Disclosure: I paid retail for all of the products used in this test, with the exception of the Sewer Solution. Valterra had provided that for an earlier test, but did not place any restrictions on how I could use it. The procedures, results, and conclusions you see are all my own.

James is a former rocket scientist, a USA Cycling coach, and lifelong fitness buff. When he's not driving the RV, or modifying the RV (or - that one time - doing both at once), you can find him racing bicycles, or building furniture, or making music. In his spare time, he works for a large IT company.

Hi there, I noticed that what ever you did the that some of the more dense material (i.e. sinkers) would remain on the bottom. Have you ever tried filling the tank from the toilet with very salty nearly saturated brine. Thus making the solution lease dense? Like floating in The Great Salt Lake. Also, the Tornado if used while starting with a full tank seems like it would keep agitating the water and might also help.

Never got that jazzed up about it that I thought about brining the black tank. Seems like it might work though. My personal thought is that the next occupants of the black tank won’t care if the place is a little messy, so I don’t go for perfect. “Not caked over” is good enough for us.

Ok, I know this is an old video, but I’m binge watching from the beginning. I can’t remember which mathematic principle it is, but isn’t going halfies infinitely never going to reach 0? So, no matter how many rinses with the Flush King (simulated) you do, it won’t really ever get that clean. That said, I’m a huge fan of “the solution to pollution is dilution”.

How about simulating a roof vent by installing a foot or two of ABS into the top of the clear tank? Then make up a wand with a length of 3/8 inch copper pipe (i.e. scale the wand to the size of the tank) ?

Uh – there is a roof vent in this video. As for the wand – testing a wand would be basically a test of where I pointed the wand. Since it’s so user-dependent, I decided not to test it. Besides, that’s not something Stef would ever allow to be carried, wet and poo-covered, through the RV…

Until this video I had not heard of the Tornado so I’m not sure of it’s spray pattern, but I’m wondering how it would work on the end of a ridged pipe and turning it into a wand. With a proper adapter on the top end, the shower head could be removed and that hose used for the water supply. That would save dragging a dirty hose through the RV. As for carrying the soiled device through the trailer, a garbage bag and a drip pan would work.

I use a different method. Dump first; leave valve open while continuing to run spray flush valve into tank; fill toilet bowl 3-5 times until flush clear. Using water flow meter put 3/4 tank of water in tank, pull valve and keep running spray flush valve into tank. CONTINUE until clear, normally two times. My spray flush valve (i.e., tornado) was factory install on discharge end of tank on my class a diesel.

Regarding the “Drain End” system like the RhinoFLEX Rhino Blaster Pro Adapter for Rinsing RV Holding Tanks and 39085, I agree just closing the valve and then filling the tank is not going to accomplish much, but if you close the valve and then fill only a gallon or so and then empty and then repeat, this will remove a lot of the stuff off the bottom which is where most of the residue resides. Sure, it won’t clean the sides, but if the idea is to get as much of solid waste out, repeat flushing with small volumes will do the job. Your video did show that after filling the tank and then draining that more of the bottom sludge was removed. Give it a try. Thanks.

Actually, I never got around to that testing. I still have the tank, and may do it some day. But really, after we got a composting toilet, the experiments became less urgent for me! (There’s a whole different field of experiments I’m thinking of related to that…)

Your tank cleaning solutions were very interesting. I’ve have a Class A motorhome that I purchased new in Oct of 1997. We travel quite a bit during the summer months utilizing the black tank and I have never cleaned the black holding tank.

I simply tilt the motorhome to one side with the onboard jacks then dump at the campground dump station as I leave the park. Then I refill the toilet about three to five times and head home. While traveling home the water slouches around and I stop at the last dump station near my home and dump for a final time. Except for an extra stop, this works for me and have no odor issues. Another point is that at the beginning of a trip I fill the toilet about three to five times before I start using the black tank.

It sounds like you’re following best practices with regards to leaving some liquid in the tank and not using the tank “dry”. That alone will prevent a lot of problems! If you’ve got something that works for you – I wouldn’t mess with success!

When running sewage through a garden hose is not required, the Flush King is the best sewage solution, but instead of buying the actual Flush King, buy the two separate parts that James had instead… this will give you more adaptability, and then you also will have the option of using either a 45 degree or 90 degree angle for the hydro flush part.

This setup will allow you to refill the tank from outside the motorhome so that you don’t have to drag a nasty hose into the motorhome or track nasty stuff on your shoes into the motorhome to refill through the toilet.

The only caveat is that your black water tank outlet would have to be capable of handling the extra weight of the setup if you plan to leave the setup permanently attached, and of course you still need to be able to close the access door, etcetera. If those things aren’t true, then you would need to remove the set up each time you finished dumping.

Hi Verla – No, I don’t have any plans to test a wand. That’d be kind of like testing a scrub brush – it would depend a lot on the user. (Plus, Stef would never let me carry a dripping toilet wand through our small Class B!)

Last time I drained the black tank, I had a stoppage and just could not clear it. I filled up the tank with the fresh water input fitting and had to stop. We left the RV park and drove home hoping the sloshing around and the chemicals breaking down everything would allow it to dump. Next day, I found a RV black tank dump site and sure enough it dumped. Now, I have a female to female hose fitting and will connect it to the 3″ Valterra end cap that has the hose male fitting. This will allow me to use the water pressure back up the drain pipe to (hopefully) dislodge whatever is plugging it up (if it ever happens again). This is a “poor man’s” solution to the device that came with the valve that you demonstrated. The 3″ end cap with a hose fitting and the female to female adapter does everything the more expensive one would do.

Well, the key to using that is: you never leave the tank completely empty so that it dries out. I never found it necessary to get the black tank “spotless”. In my opinion, the Sani-Con (the model used in the Travato) will do a far better job than the “nothing” that is installed on most RVs…

To test a wand, I’d have to blindfold myself or something to duplicate the “I can’t see down there” factor that we all have with our black tanks. That makes the whole thing seem kind of random to me. It may work one time, the next time, I might miss.

But, the real reason I haven’t tested one is that Stef has informed me in very clear terms that I will NOT be allowed to bring a wet, waste-soaked hose or wand through our RV! 🙂 That, plus the random thing kills it for me.

Great videos. I have a factory installed flush kit on my Raptor 5th wheels and it doesn’t seem to work well. Probably not a tornado. May have to do some serious digging and find out. Maybe install a Tornado as a second flush.

James, I really enjoyed watching your video on tank rinsing. I’ve questioned the effectiveness of the Hydroflush & Flush King type systems ever sense I learned of them. I’ve seriously considered installing the Tornado Rotary tank Rinser style system but after seeing your video am not sold on its effectiveness as well. A couple things I thought of that may have helped with all your tests is the bottoms of black tanks are not flat. Most are tapered toward the drain opening. I doubt this would have changed the overall results much but note worthy. Additionally, I’ve thought of use prior to dumping. If we are traveling (family of five) we defiantly use the toilet for #1 and #2 if you know what I mean. I know of MANY, RVers that will not do #2 in the RV and I think it’s silly. During those times the solid waste gets a chance to slosh around for days prior to dumping. At an RV park the waist sits in liquid for a while prior dumping depending on the length of the stay of course. I’m guessing but would say most RV trips are at least 3 days on average and probably more a couple times a season. My point is the solid waste gets the opportunity to sit and dissolve for a few days. With a tapered bottom tank a good ole dump of a full toilet with water I feel does a pretty good job in and of its self. My toilet is in the same room as the tub. I’ve removed the shower hose retainer that is on most RVs (the ring about half way up) and use that to fill the toilet bowl as a quick way to dump quickly a couple gallons of water into the tank and essentially douching the remaining tank debris at a cost of only my time. Thank you again for taking the time to post these AWESOME videos and sharing your research. YOU ROCK!!

Hi Rob. Glad you like the videos! My plexiglass fabrication skills are pretty limited, so I was happy to get a box with a tube that didn’t leak! I do attempt to compensate for the flat bottom by tilting the tank toward the opening. In the next video I make with it, you’ll see that I’ve made a sled to hold it at an appropriate angle. It’s not exactly the same as a tapered tank, but close enough to get the right idea.

When I eventually get around to testing tank additives, I am working on a “3 day weekend” test schedule of adding water and waste. Like you, I agree that there are a lot of trips of that duration.

I am looking forward to your testing of chemicals to clear a partially clogged black holding tank. I tried AQUA-CHEM twice for a week at a time. First time I used 16oz with 15gals of water. No improvement. Second time used 48oz with 6 gals of water. Still no improvement.

I am thinking about cutting a hole in the bottom of the tank to see what is going on and clean it out with a putty knife. Then how would I reseal the hole? Any suggestions ?

Yikes! I wouldn’t recommend cutting a hole in the bottom of the tank. I don’t think you’d ever get is sealed up well enough again unless you were to take it to some kind of plastics welder. But even then – I wouldn’t want to be riding behind you down the highway. Lol. There are professional tank cleaning services that can tackle the situation you describe. They use high pressure tools to blast things off and clean up. Or, you might try consulting with a “Honey Bucket” vendor. If none of those can help you, you could try a cleaning wand through the toilet (but only if your tank will still partially drain – otherwise, you’d just make things worse). Finally, I saw a suggestion once from Gary Bunzer, the RV Doctor – it involved taking a snake, and running it through a hole in the top of your sewer hose (so that the snake part is inside, but the controls are outside). Hook up the hose to dump, open your valve, and snake away. If you can clear the clog, most of the problem should still drain down the sewer hose. And yes, this permanently ruins the hose, so use a cheap one. Best of luck with the problem. I don’t envy you.

Ok, You have convinced me not to cut a hole in the bottom of the black tank. How about a slit on one side near the bottom. Then I could stick the nozzle of a power washer in there. Might be easier to seal that back up.

It is getting close to winter up here in New England and will have to wait until next spring to do much of anything.

There was a small improvement with the 2nd attempt of AQUA-CHEM. It does not take as long to drizzle and drip empty. Was thinking of putting another quart or two of AQUA-CHEM with a couple of gallons of RV antifreeze and leave it over the winter. I was wondering if I would cause and damage by putting in too much AQUA-CHEM to water ratio in the tank. When I get ready dump the tank I do fill the tank with water before I actually dump it to dilute the chemicals.

Well, if you’re determined to cut a hole, why not cut the hole for installing a tank rinsing system like the Tornado? You’d need to cut the hole near the top instead of the bottom, but you could use the hole to insert a snake or a putty knife on a stick, or something. And when you’re done, you’d have a documented procedure for sealing it up, and a tank rinsing system that tested pretty well. (You don’t have to use the Tornado, there are other tank rinsing systems that might work just as well.) The tornado is fairly inexpensive and a good add to your rig anyway. As far as higher concentrations of Aqua-Chem – I haven’t tested that. Though if it’s meant to be put in a holding tank, it’s probably safer than a high concentration of something that isn’t meant for tank use (like straight bleach). You may want to call Thetford on that one. They should be able to tell you.

I contacted Thetford concerning the concentration. They said there was no need to use more than the recomended amount. They also said that I should not leave the chemical in there over the winter.

Not sure I believe them concerning the amount of concentration. Perhaps you could test that. Would be interesting to see if it would make a difference.

There must be a real hard stack of poo in there. I believe the previous owner was on a permanent spot and left the tank open to always drain. It is a 2004 Keystone Challenger. So it may have been setting there for several years with the tank valve open.

Ah yes, the “left the tank open” pyramid. Now your problems are becoming more clear. Depending on where you are, you might try to contact a tank cleaning service. (TankTechs comes to mind.) In the long run, it might be cheaper to just bite the bullet once, rather than bottle after bottle of holding tank chemicals. I had a recommendation from The RV Geeks at one time for a product called “NoFlex Digestor”. If you want to give soaking one last try, maybe you could try that one and report back!

You know, I have thought about trying to do something like “The myth of the exploding RV toilet.” I’d have to plug up the vent stack somehow, and I wouldn’t want to use my RV or clear tank. But it might be interesting… 🙂

Greatly informative video. Your time spent on this review is appreciated. Besides demonstrating which tank rinse system is the best you have also demonstrated a design flaw in the black water tanks. If the way you have constructed your test tank is similar to the manufactured tanks, as they drain from one end, this seems to prevent the flow of debris from leaving the tank. If the tank drained from the bottom and possibly the bottom shaped like a large funnel, more like the floor of a shower stall, it would probably move the debris toward the drain pipe and exit it from the tank. Again, Great Job.

I completely agree on the “bottom drain”. And if I ever get the chance to build my own RV, I’m going to try to make that happen. One of the problems with that though, is that you need extra under-floor clearance to pull it off. Coincidentally – the most recent RV I reviewed, the Pleasure-Way Plateau XL, actually has a bottom-draining black tank! It’s the first one I’ve actually gotten footage of.

I am thinking more like a sloping ditch down the center of the tank heading into the drain end. It would increase the flow of water/debris in the area by channeling it. I am not sure about the B’s. With most other class rv’s the waste water tanks are external, underneath the cabin area. You wouldn’t want anything sticking down any amount at all that could be hit and damaged. Since all these tanks are made of molded plastic, once designed they wouldn’t be any more difficult or expensive to manufacture.

Thinking of building your own RV. My thoughts likewise. My fear is the cost of purchasing all of the necessary equipment/systems would be astronomical. The end result would be fantastic.

I would be most interested in your thoughts on this. Do you have a blog or message board (forum) on this topic. I am a DTA graduate from TSOHK. Retired. (Diversified Technological Assistant (handyman) from the The School Of Hard Knocks (past experience) apprenticed under my father for many years)

You know, just recently, we reviewed a Pleasure-Way Plateau XL which had a black tank that drained from the bottom of the tank. I thought it was brilliant. They had raised the floor in the bathroom area to be able to lift the black tank high enough. That was a B+ (small C) though. It would be much more difficult to drain out of the bottom in a true class B. But the 4×4 Sprinter, coming next year, is about 4 or 5 inches higher up. It may be high enough….

We don’t have a “build your own” forum. If I do go that route, we’ll devote a whole chunk of the website to it. But until I start on that (if I ever do), we don’t have it. Sorry!

1. Your “actual” evidence is so much more valuable than the mostly anecdotal comments provided with most product reviews. Thanks for the huge investment of time and energy.

2. I don’t understand the obsession with “spotless” black tanks. It seems to me that only two goals are important: – no odors – no plugged drain lines If these are met, what else really matters. I have seen comments about “sanitizing” the black tank. Why? I don’t plan to eat off of it. I can see cleaning/flushing the tank before winter storage, but between stops on a long trip? Why?

3. I agree with your suggestion to use the toilet to refill the tank and drain it after dumping. I am not interested in carrying a second, dedicated hose just to “clean” the tank.

4. Thanks for showing that the clear drain pipe section is a scam.

5. You did not mention it, but your trials seems to suggest that a greater slope on the bottom of the tank would improve solids removal, although this would also somewhat reduce tank volume. There is probably little or no incentive for manufacturers to consider this.

6. Looking forward to your test of tank treatments. Again, “evidence” vs “anecdotal.” Some people seem to think a black tank is a septic tank. It is not! It is a storage tank.

Hi James… I am going to take a Black Water tank out of a 5th wheel and connect it to a septic tank directly with 3″ ABS pipe. Have you done this before? Any advice in advance would be helpful. I am thinking I will need to put a vent pipe outside to make this work properly.

The 5th wheel RV will be staying on our property and will not be going on the road anymore…. Enjoyed your video’s. Thank you…..tom

Hi Tom. I’d be a bit worried with what you’re proposing. I don’t think that the venting will be your biggest issue. (Though you will need to check building codes and do whatever is required on that front.)

RV toilets use a heck of a lot less water than a household toilet. I guess it depends on the slope, but I would be worried that, without an appropriate volume of water to move things along, you might have things get “stuck” in your ABS pipe. That could be very bad.

If it were me, I would be leaving the tank in. Dumping takes only a few seconds every few days.

Very interesting series. I am looking forward to the additive testing. In fact if you will email me an address, I will send you an inexpensive, commercially available cleanser/rinsing agent that is used to clean and neutralize in ag tanks. I’ve been using it for several years in my black tank and it does appear to keep my sensors clean and functioning. Of course it is impossible for me to say that this stuff actually works as I can only give anecdotal evidence (and I can’t see into the tank).

Hey Robert – First, I have to get through the “standard” RV tank additives, which may take me a while. I intend to test “nothin’ but water”, the GEO method, the standard blue stuff in a bottle, and some sort of eco-friendly enzyme pack. Each one of those will likely take a week for me to get through. If we haven’t all lost interest by that point, I may hit you up for the “unconventional” additive. Thanks for the offer!

I’d be interested to see you try one of the probiotic tank treatments in your next experiment. I personally use the Geo method plus a Valterra Master Blaster tank wand, but I’d be interested to see if the probiotics would be beneficial.

Agree with above comment, would love to see results using tank additives PLUS the “through-the-commode” tank wands that are supposed to give you similar results to the Tornado system…without making a tank wall penetration.

Thanks for the tests so far…you’ve kept me from spending money unnecessarily on systems that obviously won’t work.

Well if I’m saving someone money then I must be doing something right! Thanks for checking us out Dennis. I’m already working on the additives experiment, but there’s a lot of prep on that one. I hope to have the setup completed in the next couple of weeks.

In addition to the Tornado rinser, how effective is just dumping bulk water (3-5 gallons) straight into the toilet to break up any solids along the bottom? I currently use the Tornado rinser and bucket of water as my cleaning procedure when cleaning my black tank.

Maybe also a test to see how effective the “bag of ice” trick is in dislodging solids? Maybe even a test of bath salts (silica salt) on the tank walls to prevent buildup? Just a few suggestions….

Since the bag of ice works in conjunction with driving around, I’d have to work up some kind of “shaker table” for the tank. I’m not sure how I would do that. Convert an old paint mixer? BUT! Some of my next tests will be of tank additives. I plan to test the GEO (water softener and detergent) solution as one of the options. I’m trying to work out the logistics of those experiments in the next couple weeks. – James

Simply great work! I use the Flush King myself, and had generally come to the conclusion that your experiment strongly supports. That is, it’s the same as refilling the tank by any other means. May be more convenient, and I do already own the thing, but not significantly contributing to the cleaning of the tank. So now I research both the Turbo and its competitors.

Can’t wait for the tank treatments experiment. Be sure and include the Geo method if you can. A whole bunch of folks swear by it.

great test series. Just a point to note. even though you used a pressure regulator on the rinse system. I actually use a Spigot tree. My rig get the regulates pressure, but my rinse system and outdoor hose with nozzle get the standard … whatever the given pressure is. I want the most pressure going throughout the rinse system.

just food for thought. great series though…. I think it’d be cool to see how the tank chems distribute and dissolve in a tank…. powders, packets, liquid chems, install a port to add them and see what happens wen the dissolve into solution

Hi Ben, Regarding the water pressure – the pressure at my house is really high, at around 120psi. When I ran my last test (with a straight discharge pipe), I got feedback that most people couldn’t expect this kind of pressure, so I put on the regulator. I agree that the performance of the Drain End rinsers might have been a bit better with higher pressure, but based on what I saw, not enough to materially affect the results. I’m curious as to how those packets dissolve myself, that should be pretty interesting in the clear tank. Thanks for watching!

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